Orthodontic treatment involves the repositioning of misaligned teeth and improving bite configurations for improved dental function and cosmetic appearance. Repositioning teeth may be accomplished by applying controlled forces to the teeth over an extended period of time. A number of systems and techniques are known for applying the required forces to the teeth.
One known method for applying forces to the teeth is by the use of elastic positioning appliances as described by Chishti et al. in U.S. Pat. No. 5,975,893. Such positioning appliances comprise a thin shell of elastic material that generally conforms to a patient's teeth but is slightly out of alignment with the initial tooth position. Placement of the positioning appliance over the teeth applies controlled forces to the teeth to gradually move the teeth into a new position. Repetition of this process with successive positioning appliances comprising new teeth positions eventually moves the teeth through a series of intermediate positions to a final desired position.
When the positioning appliance is placed over a prescribed group of teeth, one or more of the teeth may provide an anchor for holding the appliance in place while the stiffness of the appliance imparts a positioning force against at least a portion of the target teeth.
The anchoring and repositioning abilities of positioning appliances are dependent at least in part on the physical features and positions of the patient's teeth, previous dental work, and the like. Among other things, these physical features may not be optimally suitable for providing an optimal force bearing surface for anchoring or applying positioning forces to the teeth by the positioning appliance. For example, but not limited thereto, positioning appliances may have difficulty applying certain forces to individual teeth, such as extrusive forces (e.g., pulling or raising a tooth relative to the jaw).
Attempts to augment the force transfer between the positioning appliance and the teeth have been attempted, such as those described by Phan et al. in U.S. Pat. No. 7,125,248. Phan et al. describes the use of attachment devices that are bonded to one or more teeth or other dental feature so as to provide an enhanced surface upon which the positioning appliance may bear. Phan et al. describes a method of forming and bonding the attachment device to the teeth with the use of a mold. The mold is substantially in the form of the positioning appliance, which substantially conforms to the teeth, but has one or more negative impressions having a shape that is complementary to the desired attachment device. Malleable polymerizing material is placed in the negative impression and the mold slidingly received over the teeth. The polymerizing material is cured such that when the mold is removed from the teeth, the now polymerized material forms the attachment device that, if successful, is bonded to the tooth. This method is referred herein as the mold-in-place approach.
In practice, the mold-in-place approach as provided by Phan et al. has a number of shortcomings. One shortcoming, among others, is that a precise amount of the polymerizing material must be disposed within the respective negative impression otherwise the negative impression may be underfilled or overfilled. An underfilled negative impression may lead to, among other things, an underdeveloped or malformed attachment device that is not suitable for the intended purpose. Further, an underfilled negative impression may lead to, among other things, the polymerizing material making only partial or insufficient contact with the tooth surface thereby resulting in an attachment device that is partially or insufficiently bonded to the tooth. Ensuring full contact between the polymerizing material and the tooth surface is further complicated by the necessity of using a very viscous polymerizing material. The polymerizing material must be very viscous so that, among other things, the polymerizing material stays substantially within the negative impression during handling of the mold and in placement on the teeth. Being very viscous or putty-like, the polymerizing material may not flow towards the tooth surface and make full contact therewith prior to curing resulting in a poorly or not bonded attachment device.
An overfilled negative impression may lead to, among other things, an ill-fitting, distorted mold. An overfilled mold may, among other things, not seat properly on the tooth surface so as to not position the polymerizing material at the intended location and/or may form a malformed attachment device after cure. The mold may have to be forcibly held in place on the teeth to ensure that it is properly seated thereon during the curing process.
An overfilled negative impression may lead to, among other things, flashing. Flashing is excess polymerizing material that may deposit on unintended tooth surfaces and/or beyond the prescribed footprint of the attachment device. The excess material may be unintentionally deposited on the tooth surface when the mold is slidingly received onto the teeth. The excess material may extrude away from the negative impression when pressure is exerted onto the mold during placement and cure of the polymerizing material. Flashing must be removed to allow for proper placement of the positioning appliance onto the teeth. Flashing has the potential to cause, among other things, the positioning appliance to not seat properly on the teeth and may cause unintentional forces on the teeth resulting in improper repositioning. Removing flashing is labor and time intensive and may lead to damage to the resulting attachment device and/or undesirable modification of the underlying tooth surface to which it is attached.
A precisely formed attachment device is crucial for optimal performance of the positioning appliance. The shape of the positioning appliance is designed taking into account the precise position and shape of any attachment devices that may be provided. A malformed or misplaced attachment device may lead to, among other things, a malfitting positioning appliance that may result in non-prescribed or inefficient expressions of intended forces acting on one or more teeth resulting in unpredictable and undesired repositioning of the teeth.
The consequences of improperly formed attachment devices may lead to an interruption in the proposed intended sequence of progressive positioning appliances. Positioning appliances are created and supplied by the manufacturer as a set with the expectation that the attachment devices are properly formed. In many cases, the imprecise placement and formation of the attachment devices results in, among other things, inappropriate repositioning of the teeth prolonging the treatment, and requiring the manufacture of additional positioning appliances to reposition or fine-tune the repositioning of the teeth which increases the cost of materials and patient and doctor time.
It would therefore be desirable to provide apparatus and methods for forming and positioning attachment devices that address one or more of these shortcomings.